Effect of samarium doping on the activity and sulfur resistance of Ce/MnFeO_(x) catalyst for low-temperature selective catalytic reduction of NO_(x) by ammonia

The self-made MnFeO_(x) catalysts doped with cerium and samarium were prepared by impregnation method for low-temperature selective catalytic reduction(SCR)by NH3.In this work,the surface properties of the series of MnFe-based catalysts were studied.The results indicate Sm-modified catalyst have superior low-temperature SCR activity;NO_(x) conversion maintained at nearby to 100%at 90℃ to 240℃.In addition,The N_(2) selectivity of Sm doping remains above 80%in the range of 60℃ to 150℃.In SO_(2) poisoning test,the NO_(x) conversion can be remained>90%after 10 h of reaction.The XPS,NH_(3)-TPD and H_(2)-TPR results show the catalyst with Sm doping enhances the acid sites and oxidation catalytic sites of mixed oxides serves for improving oxygen vacancies and transfer electrons.In situ diffuse reflaxions infrared Fourier transformations spectroscopy(DRIFTS)results show that NO_(x) is more easily adsorbed on the surface after Sm doping,which provided favorable conditions for the NH_(3)-SCR reaction to proceed.The reaction at the catalyst surface will follow the L-H reaction mechanism by transient reaction test.

Enhancing selectivity in acidic CO_(2) electrolysis:Cation effects and catalyst innovation

The electrochemical reduction of CO_(2)(eCO_(2)R)under ambient conditions is crucial for reducing carbon emissions and achieving carbon neutrality.Despite progress with alkaline and neutral electrolytes,their efficiency is limited by(bi)carbonates formation.Acidic media have emerged as a solution,addressing the(bi)carbonates challenge but introducing the issue of the hydrogen evolu-tion reaction(HER),which reduces CO_(2) conversion efficiency in acidic environments.This review focuses on enhancing the selectivity of acidic CO_(2) electrolysis.It commences with an overview of the latest advancements in acidic CO_(2) electrolysis,focusing on product selectivity and electrocatalytic activity enhancements.It then delves into the critical factors shaping selectivity in acidic CO_(2) electrolysis,with a special emphasis on the influence of cations and catalyst design.Finally,the research challenges and personal perspectives of acidic CO_(2) electrolysis are suggested.

Tuning the product selectivity of dimethyl oxalate hydrogenation over WO_(x) modified Cu/SiO_(2) catalysts

Product selectivity and reaction pathway are highly dependent on surface structure of heterogeneous catalysts.For vapor-phase hydrogenation of dimethyl oxalate(DMO),"EG route"(DMO→methyl glycolate(MG)ethylene glycol(EG)→ethanol(ET))and"MA route"(DMO→MG→methyl acetate(MA))were proposed over traditional Cu based catalysts and Mo-based or Fe-based catalysts,respectively.Herein,tunable yield of ET(93.7%)and MA(72.1%)were obtained through different reaction routes over WO_(x) modified Cu/SiO_(2) catalysts,and the corresponding reaction route was further proved by kinetic study and in-situ DRIFTS technology.Mechanistic studies demonstrated that H_(2) activation ability,acid density and Cu-WO_(x) interaction on the catalysts were tuned by regulating the surface W density,which resulted in the different reaction pathway and product selectivity.What's more,high yield of MA produced from DMO hydrogenation was firstly reported with the H_(2) pressure as low as 0.5 MPa.

Molecular engineering binuclear copper catalysts for selective CO_(2) reduction to C_(2) products

Molecular copper catalysts serve as exemplary models for correlating the structure-reaction-mechanism relationship in the electrochemical CO_(2) reduction(eCO_(2)R),owing to their adaptable environments surrounding the copper metal centres.This investigation,employing density functional theory calculations,focuses on a novel family of binuclear Cu molecular catalysts.The modulation of their coordination configuration through the introduction of organic groups aims to assess their efficacy in converting CO_(2) to C_(2)products.Our findings highlight the crucial role of chemical valence state in shaping the characteristics of binuclear Cu catalysts,consequently influencing the eCO_(2)R behaviour,Notably,the Cu(Ⅱ)Cu(Ⅱ)macrocycle catalyst exhibits enhanced suppression of the hydrogen evolution reaction(HER),facilitating proton trans fer and the eCO_(2)R process.Fu rthermore,we explo re the impact of diverse electro n-withdrawing and electron-donating groups coordinated to the macrocycle(R=-F,-H,and-OCH_3)on the electron distribution in the molecular catalysts.Strategic placement of-OCH_3 groups in the macrocycles leads to a favourable oxidation state of the Cu centres and subsequent C-C coupling to form C_(2) products.This research provides fundamental insights into the design and optimization of binuclear Cu molecular catalysts for the electrochemical conversion of CO_(2) to value-added C_(2) products.

A critical review towards the causes of the iron-based catalysts deactivation mechanisms in the selective oxidation of hydrogen sulfide to elemental sulfur from biogas

Hydrogen sulfide(H_(2)S) not only presents significant environmental concerns but also induces severe corrosion in industrial equipment,even at low concentrations.Among various technologies,the selective oxidation of hydrogen sulfide(SOH_(2)S) to elemental sulfur(S) has emerged as a sustainable and environmentally friendly solution.Due to its unique properties,iron oxide has been extensively investigated as a catalyst for SOH_(2)S;however,rapid deactivation has remained a significant drawback.The causes of iron oxide-based catalysts deactivation mechanisms in SOH_(2)S,including sulfur or sulfate deposition,the transformation of iron species,sintering and excessive oxygen vacancy formation,and active site loss,are thoroughly examined in this review.By focusing on the deactivation mechanisms,this review aims to provide valuable insights into enhancing the stability and efficiency of iron-based catalysts for SOH_(2)S.

Building up a general selection strategy and catalytic performance prediction expressions of heteronuclear double-atom catalysts for N_(2)reduction

The severe environmental problems and the demand for energy urgently require electrocatalysis to replace Haber-Bosch for the nitrogen reduction reaction(NRR).The descriptors and important properties of single-atom and homonuclear double-atom catalysts have been preliminarily explored,but the relationship between the inherent properties and catalytic activity of heteronuclear double-atom catalysts with better performance remains unclear.Therefore,it is very significant to explore the prediction expressions of catalytic activity of heteronuclear double-atom catalysts based on their inherent properties and find the rule for selecting catalytic centers.Herein,by summarizing the free energy for the key steps of NRR on 55 catalysts calculated through the first-principle,the expressions of predicting the free energy and the corresponding descriptors are deduced by the machine learning,and the strategy for selecting the appropriate catalytic center is proposed.The selection strategy for the central atom of heteronuclear double-atom catalysts is that the atomic number of central B atom should be between group VB and VIIIB,and the electron difference between central A atom and B atom should be large enough,and the selectivity of NRR or hydrogen evolution reaction(HER)could be calculated through the prediction formula.Moreover,five catalysts are screened to have low limiting potential and excellent selectivity,and are further analyzed by electron transfer.This work explores the relationship between the inherent properties of heteronuclear double-atom catalysts and the catalytic activity,and puts forward the rules for selecting the heteronuclear double-atom catalytic center,which has guiding significance for the experiment.

High H_(2) selective performance of Ni-Fe-Ca/H-Al catalysts for steam reforming of biomass and plastic

The development of a selective catalyst for the conversion of biomass and plastics into H2by steam reforming can combat the energy crisis and global warming.In this work,support Ni-Fe-Ca/H-Al bifunctional catalysts were prepared by loading Ni and Fe into pretreatment CaO/Al_(2)O_(3)(Ca/H-Al)carriers and showed high catalytic activity for the steam reforming of biomass and plastic.Moreover,the idea of bidirectional degradation was exploited to strengthen the pyrolysis of plastic with a high H/C and biomass with a high O/C.Interestingly,the products presented high H2selective(1302.10 m L/g)and low CO_(2)yield(120.23 m L/g)in 7Ni-5Fe-Ca/H-Al(2:4)catalyst compared with current reports.Here,the abundant oxygen vacancies(Ov)in the H-Al carrier exhibited an electron-deficient nature,providing active sites for anchoring Ni O.Meanwhile,Ni O interacted with Ca_(2)Fe_(2)O_(5)to produce more defective Ovsites,which stabilized the NiO particles in the 7Ni-5Fe-Ca/H-Al(2:4)catalyst,and the interaction between the catalyst and the carrier was enhanced,leading to the reduction of weakly basic sites,this property promoted the strong adsorption of CO_(2)and H2O by the catalyst,contributing to the enhancement of efficient steam conversion and the promotion of conversion of by-products to H2.Notably,7Ni-5Fe-Ca/H-Al(2:4)catalysts maintained structural integrity after regeneration and exhibited excellent regenerability in H2selection and CO_(2)adsorption.The work provides a new idea for the study of efficient H2production from steam reforming of biomass and plastics.

Synergy of heterogeneous Co/Ni dual atoms enabling selective C-O bond scission of lignin coupling with in-situ N-functionalization

Selective cleavage of Csp^(2)-OCH_(3)bond in lignin without breaking other types of C-O bonds followed by N-functionalization is fascinating for on-purpose valorization of biomass.Here,a Co/Ni-based dual-atom catalyst CoNiDA@NC prepared by in-situ evaporation and acid-etching of metal species from tailor-made metal–organic frameworks was efficient for reductive upgrading of various lignin-derived phenols to cyclohexanols(88.5%–99.9%yields),which had ca.4 times higher reaction rate than the single-atom catalyst and was superior to state-of-the-art heterogeneous catalysts.The synergistic catalysis of Co/Ni dual atoms facilitated both hydrogen dissociation and hydrogenolysis steps,and could optimize adsorption configuration of lignin-derived methoxylated phenols to further favor the Csp^(2)-OCH_(3)cleavage,as elaborated by theoretical calculations.Notably,the CoNi_(DA)@NC catalyst was highly recyclable,and exhibited excellent demethoxylation performance(77.1%yield)in real lignin monomer mixtures.Via in-situ cascade conversion processes assisted by dual-atom catalysis,various high-value N-containing chemicals,including caprolactams and cyclohexylamines,could be produced from lignin.

Metal-organic framework-derived Co-C catalyst for the selective hydrogenation of cinnamaldehyde to cinnamic alcohol

The liquid phase selective hydrogenation of cinnamaldehyde has been investigated over the catalysts Co-C-T(T=400-700℃),which were derived from the carbonization of the MOF precursor Co-BTC at different temperatures in inert atmosphere.Co-C-500 exhibited a higher conversion(85.3%)than those carbonized at other temperatures,with 51.5%selectivity to cinnamyl alcohol,under a mild condition(90℃,4 h,2 MPa H_(2),solvent:9 ml ethanol and 1 ml water).The high catalytic activity of Co-C-500 can be ascribed to the large specific surface area of the catalyst,the uniformly dispersed metallic cobalt nanoparticles,and the more defect sites on the carbon support.Moreover,Co-C-500 showed excellent reusability in 5 successive cycles,mainly related to the uniformly dispersed cobalt nanoparticles embedded in carbon support.

Towards the selectivity distinction of phenol hydrogenation on noble metal catalysts

Selective hydrogenation of phenol to cyclohexanone is intriguing in chemical industry.Though a few catalysts with promising performances have been developed in recent years,the basic principle for catalyst design is still missing owing to the unclear catalytic mechanism.This work tries to unravel the mechanism of phenol hydro-genation and the reasons causing the selectivity discrepancy on noble metal catalysts under mild conditions.Results show that different reaction pathways always firstly converge to the formation of cyclohexanone under mild conditions.The selectivity discrepancy mainly depends on the activity for cyclohexanone sequential hy-drogenation,in which two factors are found to be responsible,i.e.the hydrogenation energy barrier and the competitive chemisorption between phenol and cyclohexanone,if the specific co-catalyzing effect of H 2 O on Ru is not considered.Based on the above results,a quantitative descriptor,E b(one/pl)/E a,in which E a can be further correlated to the d band center of the noble metal catalyst,is proposed by the first time to roughly evaluate and predict the selectivity to cyclohexanone for catalyst screening.

Improvement of High-efficiency Green Catalysts for Flue Gas Denitrification

Based on the basic principle and mechanism of flue gas denitrification,the commonly used catalysts for flue gas denitrification were introduced firstly,and then the catalytic performance,stability and reaction mechanism of catalysts in the market were analyzed.Different types of catalysts were studied to look for green catalysts with high activity,sulfur resistance,water vapor resistance and other advantages.The mechanism of denitration reaction of green catalysts was discussed,and the laws of formation,propagation and consumption of active species in the reaction process were revealed to provide theoretical basis for optimizing catalyst design and improving reaction conditions.Then the research status and problems of new catalysts for flue gas denitrification were described.Finally,the future development direction of green catalysts for flue gas denitration was discussed to improve the performance and stability of catalysts and meet the performance requirements of denitration catalysts in different industries.

Selective hydrogenolysis of biomass-derived furfuryl alcohol into 1,2- and 1,5-pentanediol over highly dispersed Cu-Al_2O_3 catalysts

Cu nanoparticles supported on a variety of oxide supports, including SiO2, TiO2, ZrO2, Al2O3, MgO and ZnO, were investigated for the hydrogenolysis of biomass‐derived furfuryl alcohol to1,2‐pentanediol and 1,5‐pentanediol. A Cu‐Al2O3 catalyst with 10 wt% Cu loading prepared by a co‐precipitation method exhibited the best performance in terms of producing pentanediols compared with the other materials. This catalyst generated an 85.8% conversion and a 70.3% combined selectivity for the target pentanediols at 413 K and 8 MPa H2 over an 8‐h reaction. The catalyst could also be recycled over repeated reaction trials without any significant decrease in productivity. Characterizations with X‐ray diffraction, NH3/CO2‐temperature programmed desorption, N2 adsorption,transmission electron microscopy and N2 O chemisorption demonstrated that intimate and effective interactions between Cu particles and the acidic Al2O3 support in this material greatly enhanced its activity and selectivity. The promotion of the hydrogenolysis reaction was found to be especially sensitive to the Cu particle size, and the catalyst with Cu particles 1.9 to 2.4 nm in size showed the highest turnover frequency during the synthesis of pentanediols.

Fe-Mn/Al_2O_3 catalysts for low temperature selective catalytic reduction of NO with NH_3

A series of Fe‐Mn/Al2O3 catalysts were prepared and studied for low temperature selective catalytic reduction （SCR） of NO with NH3 in a fixed‐bed reactor. The effects of Fe and Mn on NO conversion and the deactivation of the catalysts were studied. N2 adsorption‐desorption, X‐ray diffraction, transmission electron microscopy, energy dispersive spectroscopy, H2 temperature‐programmed reduction, NH3 temperature‐programmed desorption, X‐ray photoelectron spectroscopy （XPS）, thermal gravimetric analysis and Fourier transform infrared spectroscopy were used to character‐ize the catalysts. The 8Fe‐8Mn/Al2O3 catalyst gave 99%of NO conversion at 150？？ and more than 92.6%NO conversion was obtained in a wide low temperature range of 90–210？？. XPS analysis demonstrated that the Fe3＋was the main iron valence state on the catalyst surface and the addition of Mn increased the accumulation of Fe on the surface. The higher specific surface area, enhanced dispersion of amorphous Fe and Mn, improved reduction properties and surface acidity, lower binding energy, higher Mn4＋/Mn3＋ratio and more adsorbed oxygen species resulted in higher NO conversion for the 8Fe‐8Mn/Al2O3 catalyst. In addition, the SCR activity of the 8Fe‐8Mn/Al2O3 cata‐lyst was only slightly decreased in the presence of H2O and SO2, which indicated that the catalyst had better tolerance to H2O and SO2. The reaction temperature was crucial for the SO2 resistance of catalyst and the decrease of catalytic activity caused by SO2 was mainly due to the sulfate salts formed on the catalyst.

Resistance to SO_2 poisoning of V_2O_5/TiO_2-PILC catalyst for the selective catalytic reduction of NO by NH_3

A titania pillared interlayered clay（Ti-PILC） supported vanadia catalyst（V2O5/TiO2-PILC） was prepared by wet impregnation for the selective catalytic reduction（SCR） of NO with ammonia. Compared to the traditional V2O5/TiO2 and V2O5-MoO3/TiO2 catalysts, the V2O5/TiO2-PILC catalyst exhibited a higher activity and better SO2 and H2O resistance in the NH3-SCR reaction. Characterization using TPD, in situ DRIFT and XPS showed that surface sulfate and/or sulfite species and ionic SO4^（2-）species were formed on the catalyst in the presence of SO2. The ionic SO4^（2-） species on the catalyst surface was one reason for deactivation of the catalyst in SCR. The formation of the ionic SO4^（2-） species was correlated with the amount of surface adsorbed oxygen species. Less adsorbed oxygen species gave less ionic SO4^（2-） species on the catalyst.

Selective CO Methanation over Ru Catalysts Supported on Nanostructured TiO2 with Different Crystalline Phases and Morphology

Nanostructured titanium dioxides were synthesized via various post-treatments of titanate nanofibers obtained from titanium precursors by hydrothermal reactions. The microstructures of TiO2 and supported Ru/TiO2 catalysts were characterized with X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray analysis, and nitrogen adsorption isotherms. The phase structure, particle size, morphology, and specific surface area were determined. The supported Ru catalysts were applied for the selective methanation of CO in a hydrogen-rich stream. The results indicated that the Ru catalyst supported on rutile and TiO2-B exhibited higher catalytic performance than the counterpart supported on anatase, which suggested the distinct interaction between Ru nanoparticles and TiO2 resulting from different crystalline phases and morphology.

Selective catalytic methanation of CO in hydrogen-rich gases over Ni/ZrO_2 catalyst

Ni/ZrO2 catalysts were prepared by the incipient-wetness impregnation method and were investigated in activity and selectivity for the selective catalytic methanation of CO in hydrogen-rich gases with more than 20 vol% CO2. The result showed that Ni loadings significantly influenced the performance of Ni/ZrO2 catalyst. The 1.6 wt% Ni loading catalyst exhibited the highest catalytic activity among all the catalysts in the selective methanation of CO in hydrogen-rich gas. The outlet concentration of CO was less than 20 ppm with the hydrogen consumption below 7%, at a gas-hourly-space velocity as high as 10000 h-1 and a temperature range of 260 °C to 280 °C. The X-ray diffraction （XRD） and temperature programmed reduction （TPR） measurements showed that NiO was dispersed thoroughly on the surface of ZrO2 support if Ni loading was under 1.6 wt%. When Ni loading was increased to 3 wt% or above, the free bulk NiO species began to assemble, which was not favorable to increase the selectivity of the catalyst.

Selective catalytic oxidation of NO with O_2 over Ce-doped MnO_x/TiO_2 catalysts

A series of Ce-doped MnOx/TiO2 catalysts were prepared by impregnation method and used for catalytic oxidation of NO in the presence of excess O2. The sample with the Ce doping concentration of Ce/Mn=l/3 and calcined at 300 ℃ shows a superior activity for NO oxidation to NO2. On Ce（1）Mn（3）Ti catalyst, 58% NO conversion was obtained at 200 ℃ and 85% NO conversion at 250 ℃ with a GHSV of 41000 h-1, which was much higher than that over MnOx/TiO2 catalyst （48% at 250 ℃）. Characterization results implied that the higher activity of Ce（1）Mn（3）Ti could be attributed to the enrichment of well-dispersed MnO2 on the surface and the abundance of Mn3＋ and Zi3＋ species. The addition of Ce into MnO2/TiO2 could improve oxygen storage capacity and facilitate oxygen mobility of the catalyst as shown by PL and ESR, so that its activity for NO oxidation could be enhanced. The effect of H2O and SO2 on the catalyst activity was also investigated.

Highly selective CO methanation over amorphous Ni-Ru-B/ZrO_2 catalyst

Amorphous Ni-Ru-B/ZrO2 catalyst was prepared by the means of chemical reduction, and selective CO methanation as a strategy for CO removal in fuel processing applications was investigated over the amorphous Ni-Ru-B/ZrO2 catalyst. The result showed that, at the temperature of 210-230 ℃, the catalyst was shown to be capable of reducing CO in a hydrogen-rich reformate to less than 10 ppm, while keeping the CO2 conversion below 1.55% and the hydrogen consumption below 6.50%. ？2009 Xin Fa Dong. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

Influence of chromium modification on the properties of MnO_x-FeO_x catalysts for the low-temperature selective catalytic reduction of NO by NH_3

Catalytic properties of MnOx-FeOx complex oxide （hereafter denoted as Mn-Fe） catalysts modified with different loadings of chromium oxide were investigated by using the combination of physico-cbemical techniques, such as N2 physisorption, X-ray diffraction （XRD）, high-resolution transmission electron microscope （HRTEM）, in situ Fourier transform infrared spectroscopy （in situ FT-IR） and temperature-programmed reduction （TPR） and their catalytic activities were evaluated with the selective catalytic reduction （SCR） of NOx by NH3. It was found that with the addition of Cr, more NO could be removed in the low-temperature window （below 120 ℃）. Among the tested catalysts, Mn-Fe- Cr （2 ： 2 ： 1） catalyst exhibited the best catalytic performance at 80 ℃ with the NO conversion higher than 90%. The combination of the reaction and characterization results indicated that （1） the strong interaction among tertiary metal oxides existed in the catalysts when Cr was appropriately added, which made the active components better dispersed with less agglomeration and sintering and the largest BET specific surface area could be obtained; （2） Cr improved the low-temperature reducibility of the catalyst and promoted the formation of the active intermediate （-NH3＋）, which favored the low-temperature SCR reaction.

Study on the Nanosized Amorphous Ru-Fe-B/ZrO_2 Alloy Catalyst for Benzene Selective Hydrogenation to Cyclohexene

A novel nanosized amorphous Ru-Fe-B/ZrO2 alloy catalyst for benzene selective hydrogenation to cyclohexene was investigated. The superior properties of this catalyst were attributed to the combination of the nanosize and the amorphous character as well as to its textural character. In addition, the concentration of zinc ions, the content of ZrO2 in the slurry, and the pretreatment of the catalyst were found to be effective in improving the activity and the selectivity of the catalyst.